Stages are built to maximize contact between incoming vapor and incoming liquid. During contact, some of the light component in entering liquid is vaporized and leaves with vapor. At the same time, some of the heavy component in the entering vapor condenses and leaves with the liquid.
Ideal stage is the one where vapor and liquid leave the stage in equilibrium. In ideal stage, it is assumed that liquid stream leaving the plate are in bubble point while vapor stream leave at their dew point.
When no azeotropes are present, both up and bottom products may be obtained in any desired purity if enough stages are provided and enough reflux is available. In practice, there are limits to number of stages and to amount of reflux. Therefore, not every separation can be accomplished. Theoretical limits on performance are imposed by total reflux (minimum stages) and minimum reflux (infinite number of ideal stages).
Name : Pratiksha Shrestha
Ms. Shrestha holds masters degree in food engineering and bioprocess technology from Asian Institute of Technology (AIT) Thailand. She is currently working for Government of Nepal at Department of Food Technology and Quality Control (DFTQC), Kathmandu. She is also a teaching faculty in College of Applied food and Dairy Technology (CAFODAT) affiliated to Purbanchal university, Nepal.